Background-Explanation: A sound can be described by a list of articulatory features: If the list is sufficient to determine the function of the sound in a particular language, it matches the requirement of phonology, that means not a specific sound has been described, but a class of sounds that fullfill this function, though not identical. For instance, /a/ read by child, male, woman, man with a sorethroat, dwarf, giant etc. is nevertheless recognized as this particular vocal described by a few features (like: openness, nasality vs. orality, position of the root of the tongue etc.)
All features that are of no importance for describing a sounds function in a language are called redundant features. But exactly some of those redundant features are characteristic to describe the persons characteristical voice.
Just imagine, you could by a list of such redundant features capture a voice that could be described as "sounds like Barack Obama", "sounds like Nick Nolte", "sounds like Dave Chapelle", or less specific "sounds like a middle aged, tall white man from the south with a high testosterone level and missing upper front teeth".
Question: What are, or what are possible canditates for these redundant features to describe a sound more characteristically than in phonology?